2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/226965Rapidly moving sources create pairs in the vacuum and lose energy. In consequence of this, the velocity of a charged body cannot approach the speed of light closer than a certain limit which depends only on the coupling constant. The vacuum back-reaction secures the observance of the conservation laws. A source can lose up to 50% of energy and charge because of the vacuum instability.52 pages including 6 figures. Latex 2.09. Figures by METAFONT, 300 DPI. Keep all files in a separate directoryHigh Energy Physics - TheoryGeneral Relativity and Quantum Cosmologytext